I. Field of the Invention
The present invention relates to data transmissions. More particularly, the present invention relates to method and apparatus for adjusting the phase of a received signal to account for phase shifts and discontinuities experience by the signal.
II. Description of the Related Art
In a typical RF communications system, data is proceed at a transmitter device, modulated, filtered, amplified, and transmitted to one or more receiver devices. The transmitted signal typically experiences path loss, multipath, and other phenomena prior to reaching the receiver devices. At a receiver device, the modulated signal is received, conditioned, and demodulated to recover the transmitted data. The signal conditioning typically includes low noise amplification, filtering, automatic gain control, frequency downconversion, sampling, quantization, and so on.
Due to path loss, multipaths that may add constructively or destructively, and other phenomena, the signal level of the received signal typically varies over a wide rang of values. For example, for a CDMA system, the received signal may vary over 85 dB. To provide a signal having the proper level for sampling and quantization, multiple gain stages are usually employed in the received signal path. These gain stages may include one or more variable gain amplifiers (VGAs) having gains that can be adjusted by control signals. The receive signal path may also include one or more sections in which the received signal can be routed through one of several signal paths (e.g., a gain path and a bypass path).
The characteristics of the received signal can change as the variable circuit elements in the receive signal path are adjusted or as different signal paths are selected. In particular, the phase of the received signal can shift as the circuit elements are adjusted. The received signal can have phase discontinuities if the circuit elements are adjusted in a step-wise fashion or if the signal is switched through different signal paths. The phase shifts and discontinuities can cause performance degradation.
Conventionally, changes to the phase of the received signal are maintained at acceptable levels by proper design and operation of the circuit elements in the receive signal path. For example, some conventional designs limit the rate at which the circuit elements and signal paths can be switched. These limitations allow the loops in the receive signal path to better track the changes, thereby reducing the amount of degradation. However, these limitations also prevent the receiver device from tracking fast changes in the received signal, which may also degrade performance. Furthermore, in CDMA systems, these limitations may also adversely affect the initial transmit power level.
As can be seen, techniques for adjusting the phase of a received signal to compensate for phase shifts and/or discontinuities due to adjustments and/or switching of circuit elements associated with the receive signal path are highly desirable.